how to apply texture paint
You first need to create the UVs. You need to unwrap your uvs. Enter edit mode. Select  the base of the neck in a loop at the base using edges. press CTRL+E >Edge Data>Mark Seam. Unselect all. Now make an edge selection starting from the base of the neck (in the middle of the loop you just selcted but starting at the middle of the neck, and select edges all the way up to the top of the head) CTRL+E>Mark edges.
Now: Select all: CTRL+U (unwrap) while still on EDIT mode. Then you have a UV map. Finally apply the texture you created. You´ll get distorted things. Start painting again, only this time you will see your UVs and your Material and Your textures.

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BFCT_Schiller